Influence of foliar fertilisation with calcium fertilisers on the firmness and chemical composition of two highbush blueberry cultivars

Maintaining the high quality of fruits after harvest, which amongst other things is determined by firmness, is the aim producers strive after. Calcium, which fruits can be enriched with also in an extraradicular manner, is mostly responsible for the mechanical resistance of fruits. In the research conducted at the Laboratory of Orcharding, West Pomeranian University of Technology in Szczecin, the influence of foliar calcium fertilisers on the quality of fruits from two cultivars of highbush blueberry was studied. The firmness, size and chemical composition of fruits were examined (the content of mineral and organic compounds, especially polyphenols). At the fruit growth stage, bushes were sprayed 4 times with calcium solutions every 10 days, starting from the first decade of June. All fertilisers caused an increase in calcium concentrations in fruits (0.12-0.15 g 100 g-1), as compared with the control (0.09 g 100 g-1). The weight of 100 fruits collected from bushes sprayed with the Lebosol, Folanx and Calcinit fertilisers was the highest and it ranged from 327 to 365 g, and the Sunrise cultivar fruits were larger. The firmest (391 and 415 G mm) and the most resistant to mechanical damage (132 and 114 G mm) were the fruits sprayed with the calcium chloride and Folanx fertilisers, while fruits sprayed with Folanx and Calcinit were characterised by the highest polyphenol content (300 and 313 mg 100 g-1), and anthocyanins, among which delphinidin-3-galactoside predominated, constituted the largest group of compounds (77-80%). The Calcinit and Lebosol Calcium Forte fertilisers had the greatest influence on the change of chemical composition of the fruits, while the Folanx fertiliser had the greatest influence on the increase in fruit firmness. All calcium-based fertilisers decreased the acidity of fruits and, except for calcium chloride, they increased the nitrite level.